1. Field of the Invention
The present invention generally relates to propulsion systems. More particularly, the invention relates to a pulse detonation wave engine detonation initiation system having an optical ignition subsystem.
2. Technical Background
Modern day propulsion systems are used in both aerospace and military applications for a number of different purposes. For example, the aerospace industry typically requires propulsion systems to operate in a “rocket” mode (i.e. carrying oxidizer on-board) in order to drive large boost vehicles as well as smaller upper stage systems. Similarly, the defense industry generally requires propulsion systems to operate in an “air breathing” mode in order to drive missiles, etc. Additionally, a mixed system could use an air-breathing first stage and a rocket-mode upper stage for space access. Thus, propulsion systems can be used for high mass payloads as well as in situations where the payload is dominated by the fuel/oxidizer mass being used by the propulsion system. Traditionally, steady flow engines have been used in each of these types of applications. The pulse detonation wave engine (PDWE) uses, however, an alternative type of detonation cycle to achieve the same propulsion results.
The primary component of the PDWE is the combustion chamber (or detonation tube). The PDWE represents an attractive propulsion source since its engine cycle is thermodynamically closest to that of a constant volume reaction. As such, it is a minimum entropy generating device. This characteristic leads to the inference that a maximum of the potential energy of the PDWE is put into thrust and not into flow work. Thus, it follows that in order to increase thrust in this type of engine, the volume must be increased. Early approaches to the PDWE therefore focused on increasing the volume of a single combustion chamber.
More recently, the technical community has increasingly adopted the alternative choice of increasing total volume by designing the engine to include a set of banks of smaller combustion chambers. This technique, however, increases the complexity of the ignition subsystem because the inter-chamber timing must be considered.
Current approaches to igniting the PDWE have involved separate shock or blast wave initiators and chemical additives designed to enhance detonability. The blast wave detonator approach involves the use of a predetonation chamber connected to the main chamber. The predetonation chamber uses oxygen instead of air to increase reactivity and transmits a “blast wave” into the main chamber for ignition purposes. A particular difficulty associated with this technique is that the separate chamber leads to increased volume and weight. In air-breathing applications, special tanking is required for the oxygen. Furthermore, since the modern PDWE has a number of banks and chambers, ignition timing can be problematic. It is therefore desirable to provide a PDWE that does not rely upon shock wave detonation.
Highly reactive additives have also been used with the more traditional spark ignited PDWE as well as with the shock wave detonation technique. Additives work via a chemical reactivity enhancement mechanism and can be either mixed in with the fuel or added to the combustion chamber separately. Mixing the additive in with the fuel presents storage problems, while adding the additive in separately increases tankage.